(Field of the Invention)
The present invention relates to a hydrogen production apparatus and a hydrogen production method.
(Description of the Related Art)
Conventionally, a hydrogen production apparatus for producing hydrogen to be supplied to a fuel-cell vehicle or a domestic fuel cell has been proposed. For example, JP2002-255510A discloses an example of such a hydrogen production apparatus.
The hydrogen production apparatus disclosed in JP2002-255510A has the following configuration: raw material gas composed of hydrocarbon gas such as city gas, LP gas, or the like is desulfurized by a desulfurizer, and then, a reforming reaction is caused to occur to the raw material gas and water vapor by a reformer, whereby hydrogen-rich reformed gas is generated; from the reformed gas thus generated, CO2 is removed by a CO2 remover, and then, CO is removed therefrom in a transformation reaction by a CO transformer; thereafter, CO is removed by a pressure swing adsorption (PSA) purification apparatus, whereby high-purity hydrogen is taken out. In JP2002-255510A, the following remover is disclosed as an exemplary preferable CO2 remover for removing CO2 from high-temperature reformed gas: a remover that uses a solid absorbent made of an oxide ceramic that can absorb CO2 at a high temperature in the vicinities of the temperature of the reformed gas so as to cause the solid absorbent to absorb CO2 from the reformed gas, thereby removing CO2 therefrom.
In recent years, with a view to preventing global warming and the like, techniques for not releasing into atmosphere but collecting CO2 removed from reformed gas in hydrogen production process, and storing the same underground or the like, have been studied and developed. In the case of the hydrogen production apparatus disclosed in JP2002-255510A described above, however, it is necessary to apply a large amount of energy in order to collect CO2 absorbed in the absorbent of the CO2 remover.
More specifically, in order to collect CO2 absorbed in an absorbent, commonly, the absorbent is heated so as to be caused to release CO2, and here, it is necessary to heat the absorbent to a temperature higher than the reaction temperature of the absorption reaction when the absorbent absorbed CO2. This requires to apply a large amount of energy. In particular, as is the case with JP2002-255510A, in the case where a solid absorbent that can absorb CO2 at a high temperature is used and is caused to absorb CO2 from a reformed gas at a high temperature, it is necessary to heat the solid absorbent to a very high temperature so as to cause the solid absorbent to release CO2, and consequently, it is necessary to apply a very large amount of energy.
The present invention was made in order to solve the above-described problem, and it is an object of the present invention to provide a hydrogen production apparatus and a hydrogen production method with which it is possible to reduce energy applied for separation and collection of CO2 that is involved in the production of hydrogen.
In order to achieve the above-described object, a hydrogen production apparatus according to the present invention includes: a reformer that causes a reforming reaction to occur between hydrocarbon and water vapor so as to generate CO and hydrogen; a heating device that heats the reformer so as to cause the reforming reaction to proceed; a transformer that causes a transformation reaction of CO in reformed gas generated by the reformer that contains CO and hydrogen, with water vapor, so as to generate hydrogen and CO2; a hydrogen separation device that separates and takes out hydrogen from transformed gas generated by the transformation reaction that contains hydrogen and CO2; a CO2 separation device that separates and takes out CO2 from off-gas that is gas remaining after hydrogen is separated from the transformed gas by the hydrogen separation device; a heat collecting device that collects at least one among heat of the reformed gas, heat of the transformed gas, and waste heat from the heating device; and a heat supply device that supplies heat collected by the heat collecting device to the CO2 separation device, wherein the CO2 separation device includes: a capturing unit that captures CO2 in the off-gas with use of a capturing agent that absorbs or adsorbs CO2; and a heating unit that heats a capturing agent after capture that is the capturing agent after capturing CO2, by utilizing heat supplied from the heat supply device, in order to cause the capturing agent after capture to release CO2, thereby taking out CO2 therefrom.
In this hydrogen production apparatus, the heat collecting device collects at least one among heat of reformed gas, heat of transformed gas, and waste heat from the heating device heating the reformer; the heat supply device supplies heat collected by the heat collecting device to the CO2 separation device; the capturing unit of the CO2 separation device captures CO2 in off-gas after hydrogen separation with the capturing agent; and the heating unit of the CO2 separation device heats the capturing agent after capture by utilizing heat supplied from the heat supply device, in order to cause the capturing agent after capture, which has captured CO2, to release CO2, whereby taking out CO2. Thus, by utilizing at least one among heat of the reformed gas, heat of the transformed gas, and waste heat from the heating device, CO2 can be caused to be released from the capturing agent after capture. This makes it possible to save energy to be additionally applied for causing the capturing agent after capture to release CO2 so that CO2 is taken out. In this hydrogen production apparatus, therefore, energy applied for separation and collection of CO2, which is involved in the hydrogen production, can be reduced.
In the hydrogen production apparatus, the heat collecting device preferably includes a waste heat collection unit that collects waste heat from the heating device.
Waste heat from the heating device for heating the reformer is usually disposed of, but with this configuration, the waste heat to be disposed of can be collected, and the collected waste heat can be supplied by the heat supply device to the CO2 separation device so as to be effectively utilized for heating the capturing agent after capture by the heating unit. This makes it possible to further reduce energy costs.
In the hydrogen production apparatus, preferably, the heat collecting device includes a heat storage unit that stores collected heat, and the heat supply device supplies the heat stored in the heat storage unit to the heating unit.
With this configuration, for example, even if the amount of hydrogen production sharply increases, which results in that throughput per unit time for causing the capturing agent after capture to release CO2 in the CO2 separation device sharply increases, leading to a sharp increase in the amount of heat needed for heating the capturing agent after capture in the heating unit, it is possible to cope with the sharp increase in the amount of needed heat, with the heat stored in the heat storage unit.
In the hydrogen production apparatus, preferably, the heat collecting device includes a heat absorption processing unit that causes heat medium to absorb at least one among the heat of the reformed gas, the heat of the transformed gas, and the waste heat from the heating device, the heat supply device includes a heat medium supply device that supplies the heat medium having absorbed heat to the heating unit, and the heating unit heats the capturing agent after capture by imparting, to the capturing agent after capture, heat of the heat medium supplied from the heat medium supply device.
In this configuration, as heat is supplied to the heating unit by supplying the heat medium having absorbed at least one among the heat of the reformed gas, the heat of the transformed gas, and the waste heat from the heating device to the heating unit, the amount of heat lost in the process of heat supply to the heating unit can be reduced, as compared with, for example, the case where at least one among the heat of the reformed gas, the heat of the transformed gas, and the waste heat from the heating device is supplied to the heating unit by heat conduction. In other words, in the case where heat is supplied via a heat transfer member by heat conduction to a heating unit, relatively much heat is lost from the heat transfer member in the process of heat conduction, whereas the amount of lost heat can be controlled by supplying the heat medium itself having absorbed heat to the heating unit, as is the case of the present configuration.
In this case, preferably, the capturing agent is absorption liquid that is capable of absorbing CO2 from the off-gas, the capturing unit is an absorption processing unit that causes the absorption liquid to absorb CO2 in the off-gas, the CO2 separation device includes a releasing unit provided with a release flow passage that, while allowing absorption liquid after absorption that is the absorption liquid having absorbed CO2 in the absorption processing unit to flow therethrough, causes the absorption liquid after absorption to release CO2, the heating unit includes a heat medium flow passage that allows the heat medium supplied from the heat medium supply device to flow therethrough in such a manner that the heat medium exchanges heat with the absorption liquid after absorption flowing through the release flow passage, and both of the release flow passage and the heat medium flow passage are microchannels.
With this configuration, the amount of heat exchange per unit flow amount between the absorption liquid after absorption and the heat medium can be increased by heat exchange between the absorption liquid after absorption flowing through the release flow passage, which is a microchannel, and the heat medium flowing through the heat medium flow passage, which is a microchannel. This makes it possible to increase the amount of heat per unit flow amount imparted from the heat medium to the absorption liquid after absorption. Consequently, in the releasing unit, the amount of CO2 per unit flow amount released by the absorption liquid after absorption can be increased, whereby the efficiency of release of CO2 from the absorption liquid after absorption in the releasing unit can be improved.
In the hydrogen production apparatus, preferably, the heating device includes a burner that burns off-gas from which CO2 is removed by the capturing agent capturing CO2, so as to generate heat for heating the reformer.
With this configuration, fuel to be consumed for heating the reformer can be saved.
Further, a hydrogen production method according to the present invention includes: a reforming step of, while heating hydrocarbon and water vapor, causing a reforming reaction to occur between the hydrocarbon and the water vapor so as to generate CO and hydrogen; a transforming step of causing a transformation reaction of CO in the in reformed gas generated in the reforming step that contains CO and hydrogen, with water vapor, so as to generate hydrogen and CO2; a hydrogen separation step of separating and taking out hydrogen from transformed gas generated in the transformation step that contains hydrogen and CO2; a heat collecting step of collecting at least one among heat of the reformed gas, heat of the transformed gas, and waste heat of the heat used for heating hydrocarbon and water vapor in the reforming step; and a CO2 separating step of separating and taking out CO2 from off-gas that is gas remaining after hydrogen is separated from the transformed gas by the hydrogen separation step, wherein the CO2 separating step includes: a capturing step of capturing CO2 in the off-gas with use of a capturing agent that absorbs or adsorbs CO2; and a releasing step of causing a capturing agent after capture that is the capturing agent after capturing CO2 to release CO2 thereby taking out CO2 therefrom, wherein the releasing step includes a heating step of heating the capturing agent after capture by utilizing heat collected in the heat collecting step in order to cause the capturing agent after capture to release CO2.
In this hydrogen production method, at least one among heat of reformed gas, heat of transformed gas, and, waste heat of the heat used for heating hydrocarbon and water vapor in the reforming step is collected, and the capturing agent after capture is heated by utilizing the collected heat, so as to cause CO2 to be released from the capturing agent after capture in the heating step in the release step. This makes it possible to save energy to be additionally applied for causing the capturing agent after capture to release CO2 so that CO2 is taken out. In this hydrogen production apparatus, therefore, energy applied for separation and collection of CO2, which is involved in the hydrogen production, can be reduced.
In the hydrogen production method, preferably, in the heat collecting step, waste heat of heat used for heating hydrocarbon and water vapor in the reforming step is collected.
With this configuration, the waste heat that is disposed of usually can be collected, and the collected waste heat can be effectively utilized for heating the capturing agent after capture in the heating step. This makes it possible to further reduce energy costs.
In the hydrogen production method, preferably, the heat collecting step includes a heat storing step of storing collected heat in a heat storage unit, and in the heating step, the capturing agent after capture is heated by utilizing heat stored in the heat storage unit in the heat storing step.
With this configuration, for example, even if the amount of hydrogen production sharply increases, which results in that throughput per unit time for causing the capturing agent after capture to release CO2 in the releasing step in the CO2 separating step sharply increases, leading to a sharp increase in the amount of heat needed for heating the capturing agent after capture, it is possible to cope with the sharp increase in the amount of needed heat, with the heat stored in the heat storage unit.
In the hydrogen production method, preferably, the heat collecting step includes a heat absorbing step of causing heat medium to absorb at least one among the heat of the reformed gas, the heat of the transformed gas, and the waste heat, the hydrogen production method further comprising: a heat medium supplying step of supplying the heat medium having absorbed heat in the heat absorbing step to a heating unit for heating the capturing agent after capture in the heating step, wherein in the heating step, heat of the heat medium supplied to the heating unit in the heat medium supplying step is imparted to the capturing agent after capture, whereby the capturing agent after capture is heated.
In this configuration, as heat is supplied to the heating unit by supplying the heat medium having absorbed at least one among the heat of the reformed gas, the heat of the transformed gas, and the waste heat from the heating device, to the heating unit, the amount of heat lost in the process of heat supply to the heating unit can be reduced, as compared with, for example, the case where at least one among the heat of the reformed gas, the heat of the transformed gas, and the waste heat from the heating device is supplied to the heating unit by heat conduction by the heat supply device.
In this case, preferably, the capturing step includes a CO2 absorbing step of absorbing CO2 in the off-gas by using, as the capturing agent, absorption liquid that is capable of absorbing CO2 from the off-gas, in the releasing step, while absorption liquid after absorption that is absorption liquid having absorbed CO2 in the CO2 absorbing step is caused to flow through a release flow passage that is a microchannel, the absorption liquid after absorption is caused to release CO2, and in the heating step, while the heat medium having absorbed heat in the heat absorption step is caused to flow through a heat medium flow passage that is a microchannel, the heat medium is caused to exchange heat with absorption liquid after absorption flowing through the release flow passage, whereby the absorption liquid after absorption is heated.
With this configuration, the amount of heat exchange per unit flow amount between the absorption liquid after absorption and the heat medium can be increased by heat exchange between the absorption liquid after absorption flowing through the release flow passage, which is a microchannel, and the heat medium flowing through the heat medium flow passage, which is a microchannel. This makes it possible to increase the amount of heat per unit flow amount imparted from the heat medium to the absorption liquid after absorption. Consequently, in the releasing step, the amount of CO2 per unit flow amount released by the absorption liquid after absorption can be increased, whereby the efficiency of release of CO2 from the absorption liquid after absorption in the releasing step can be improved.
In the hydrogen production method, preferably, the reforming step includes a heat generating step of burning off-gas from which CO2 is removed by the capturing agent capturing CO2 in the capturing step, so as to generate heat for heating hydrocarbon and water vapor.
With this configuration, fuel to be consumed for heating hydrocarbon and water vapor in the reforming step can be saved.
As described above, with the hydrogen production apparatus and the hydrogen production method of the present invention, energy applied for separation and collection of CO2, which is involved in the hydrogen production, can be reduced.